Vortex excitations of superfluids [1]} play a crucial role
in a variety of phenomena such as the
Berezinskii-Kosterlitz-Thouless (BKT) transition, the Kibble-Zurek
(KZ) mechanism, the formation of Abrikosov vortex lattices and the
the drag force on objects moving through a superfluid. These
phenomena have been experimentally studied on a number of physical
platforms such as superconductors, liquid helium and ultracold
atoms [2]}. What all these systems have in common is that
they are up to a very good approximation in (local) thermal
equilibrium, a condition that is typically broken in experimental
platforms that are based on optical
systems [3]}, [4]}. Optical Bose-Einstein
condensates (BECs) have been experimentally achieved in optical
cavities filled with a dye molecule solution and in microcavities
where a photon is strongly coupled to an exciton resulting in
exciton-polariton [5]}. While in the latter system,
interactions between exciton-polaritons can lead to stimulated
scattering into the ground state, in the photon-dye system it is
repeated absorption and reemission of photons [6]}
that enables a macroscopic occupation of the ground
state [7]}, [8]}, [9]}.
